Get 2 m-am? +3=2㏑n-an？ +3

Get a (n? -m？ )=2(㏑n-㏑m)

Find a=2(㏑n-㏑m)/n? -m？

Observe four options, optional m= 1/n=3, 4, 5; And m = 2/n = 4.5.

1 1. Substituting into the above formula shows that the maximum value of A is ㏑ 3/4, so item B is selected.